| The sewage sludge compost land use has been attracted extensive attention for it is one of the most economical, social and environmental benefits methods to solve the problem of sludge disposal. Adding composted sludge would change the physical and chemical properties of soil, and have a significant impact on the adsorption and desorption of organic contaminants in soil. Different composting time may make different organic components in composts, thus the study of changes of the properties and the adsorption/desorption ability of organic matter under different composting time will provide a theoretical foundation for the application of sludge compost in soil organic pollution control. In this paper, Aerobic composting of sewage sludge mixed with straw and saw dust was carried out. The humic acid (HA), humin (HM) and fulvic acids (FA) under different composting time were extacted, and pentachlorophenol (PCP) was choosed as representative pollutant to discover the adsorption/desorption properties of PCP on composts, HA, HM, HM+HA and HM+HA+FA. The relationship between the changes of organic matter and the adsorption/desorption ability of PCP has been researched. The main conclusions are as follows:(1) During the composting process, the contents of total carbon, FA and HMin two treatment decreased, however the humic acid content increased. The surface area and pore volume of two composing treatments decreased, and the content of carbohydrate, aromatic compound, carboxyl, lactone, phenolic and quinonyl groups also decreased. However, the specific surface area and pore volume of HA and HM increased, and the degree of aromatization of enhanced. Functional group determination results indicated that the content of carboxyl, lactone, phenolic and quinonyl groups in HA and HM increased during the composting process.(2) The adsorption kinetic curve indicated the adsorption of PCP on compost, HA and HM could achieve balance in24h. The order of sorption capacity of PCP on three substances was HM> compost> HA. The sorption capacity of PCP on compost decreased with the extension of composting time for the reduced of the content of organic matter. The sorption ability of the HA and HM were increased, which was correspond with the increase of the aromatization degree, the specific area and pore volume. The adsorption capacity of sawdust compost was stronger than straw compost.(3) The sorption capacity of HM+HA and HM+HA+FA system decreased during the composting process. The sorption capacity of PCP onto different system was:HM> HM+HA>HM+HA+FA> HA. This result can be attributed to the fact that HA and FA molecules could compete with PCP for available sorption sites and block the micropores on the HM surfaces when HM, HA and FA exist in the same system. The contributions of HA, HM, HM+HA and HM+HA+FA on the sorption increased during composting process.(4) The two-compartment first-order model could be fit the data of Tenax-mediated desorption of PCP from compost, HA, HM, HM+HA and HM+HA+FA, and it could be described by three parts (fast, slow, non-desorption). The desorption amount of PCP on different system is:HA>Compost>HM+HA+FA> HM+HA> HM. With the extension of composting time, the desorption amount and fast desorption proportion of HA and HM decreased, the slow and non-desorption proportion increased. The desorption amount and fast desorption proportion of compost, HM+HA and HM+HA+FA increased, however slow and non-desorption proportion decreased. The phenomena were consistent with the variation of the character of organic matter. The desorption kinetics parameters has a good linear correlation with adsorption parameters, indicating the adsorption capacity determines the capacity of remain contaminant. So the desorption amount and bioavailability of contaminants could be calculated by sorption parameters.(5) The comparisons between desorbed fractions after short desorption intervals (6,12,24,48h) and the rapid desorption fraction of PCP in compost, HA, HM, HM+HA and HM+HA+FA were conducted, and showed a good correlation between them. So48,6,12,6and12hour desorption can be used to estimate the rapid desorption proportion of compost, HA, HM, HM+HA and HM+HA+FA respectively to simplify the cumbersome experimental steps of Tenax-mediated desorption. |
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